Many conventional copiers generate ammonia vapor from an aqueous ammonia solution with a heater. The current practice on such copiers is to link the input flow rate of aqueous ammonia solution and the power of the vaporizing heater to the copier's printing speed. The ammonia entering at the input flow rate is then distributed over the heater, which extends over the width of the copier, to create the ammonia vapor requirement for the material being developed; the resulting weakened concentration of aqueous ammonia being overflowed to waste.
Disadvantages of this conventional method are that it:
meters the aqueous ammonia input rate, which is inherently inexact due to the very small changes in aqueous flows which needs to be sensed, and is further complicated by the variation in rate and concentration of the waste flow,
has a limited reserve capacity for ammonia vapor which leads to vapor starvation when long lengths of material are being developed,
requires a lengthy warm-up period between switching on the copier and the initial print, plus a significant pause between speed selection and printing of long lengths of material to allow the copier to settle to the new setting,
consumes ammonia while the copier is idling, even though no material is being processed, thus contributing to an ammonia odor in the vicinity of the copier and excessive consumption of ammonia,
requires space heaters to avoid re-condensation of the vaporized ammonia, which together with the speed regulated vaporizing heater results in an excessive total power consumption rate,
discards to waste a solution still containing a fairly high percentage of ammonia which also contributes to an excessive consumption of ammonia,
requires a lengthy shut-down period to scavenge the developer tank of ammonia vapor to avoid condensation.
Broadly, to enable amelioration of at least some of these disadvantages, one aspect of this invention utilizes a control of the pressure of the gaseous developing agent with which copy material is treated, in place of controlling the flow rate of a solution of it. The invention provides, in this aspect, apparatus for developing exposed copy material wherein a gaseous developing agent is passed from a reservoir through a gas governor which functions to reduce its pressure to a set lower value, and thence into a chamber with an apertured or porous surface past which the copy material to be developed travels. Preferably the developing agent is also passed through a valve means operative to admit the vapor to that chamber only when required.